The transmission electron microscope is applied to problems directly or peripherally related to neoplasia. A major effort has been a study of the lamella-particle complex which has been found in human and animal lymphoma cells and human term placenta. It has also been recognized in tissue culture cells infected with Herpesvirus saimiri and as an apparently normal component of the horizontal cells of the human and beagle retina. Characterization of a hematopoietic stem cell in human peripheral blood is being attempted. The electron microscopy of a snake chondrosarcoma has been completed.